The rapid growth and widespread use of the Internet has brought with it an increased threat of hacker attacks on systems and/or networks coupled to the Internet, such as, for example, Local Area Networks (LANs). Such attacks may compromise sensitive information and/or destroy data. As a result, a number of companies such as Axent (Rockville, Md.), Internet Security Systems (Atlanta, Ga.), and Network Flight Recorder (Rockville, Md.) have developed Intrusion Detection Systems (IDS).
An IDS attempts to detect hacker intrusions by monitoring network traffic. A key capability of the IDS involves filtering network packets for the purpose of identifying packets exhibiting characteristics of known hacker attacks. Filtering may require identifying specific values in various fields of a protocol header, referred to as header filtering; as well as identifying character strings within a payload portion of the packet, referred to as string filtering.
There are hundreds of known strings associated with hacker attacks, and the number is rapidly increasing. Much of the processing power in an IDS is devoted to searching all incoming payloads for matches of such known strings. Current IDS products are typically software-based, and may provide acceptable packet filtering performance on networks up to 100 Mbits/sec. However, processors within an IDS often become overwhelmed when network-data traffic rates exceed 30 Mbits/sec, and hence a 100 Mbit/sec Ethernet network may exceed the ability of an IDS to protect it.
Current IDSs are unable to protect high speed LANs running at 1000 Mbits/sec. They are also unable to protect networks at Internet access points, where speeds of 155 Mbits/sec and 622 Mbits/sec are common. Some companies are providing hardware support to improve IDS performance at higher speeds. However, the packet-filtering methods employed are conventional, and limited in their extensibility to high-speed networks.
A number of known string search methods exist, including those based upon the Rabin-Karp, the Knuth-Morris-Pratt, and the Boyer-Moore algorithms. These methods are designed to search for a single string, and must be executed once for each string in the filter set. It is common for IDS filters to contain hundreds of strings, and processors can quickly become overwhelmed.